It's been known for many years that given a supply of bomb-grade material, almost anyone with access to reasonable industrial capacity could whomp up a workable nuclear weapon.

When it was said prior to the war that Iraq was just months away from a bomb if it could obtain a supply of fissile material, many on the Left hooted in derision for weeks. Of course, they didn't know what the hell they were talking about, and this current story is just further proof.

A big danger has always been that a rogue nation acquiring a supply of bomb-grade material could build a bomb with few signs that this is being done. Most of the signs of a nuclear program involve the large facilities required to process the fissionables from lower grade materials (like yellowcake). If a load of U-235 or plutonium arrives from somewhere else in a big crate, everthing else could be done in a small machine shop.

This is one reason why it's important that nations like Iran or North Korea don't start turning out bomb material. It's been hard enough keeping track of the crap that was left over in the old Soviet Union, and I'm not sure how well that was done.